1. Field of the Invention
The present invention relates generally to power tools, and more particularly, to an automatic screw feeding apparatus for a power screwdriver.
2. Description of the Related Art
A conventional screw feeding apparatus is mounted to a power screwdriver. When a user is operating the power screwdriver to screw screws onto a workpiece, a screw belt carrying a bunch of screws is automatically driven for movement along a fixed path and then the screws are conveyed to a front side of a screwdriver bit of the power screwdriver in turn to be driven by the driver bit for screw with the workpiece. In this way, the user does not have to put the screws one by one to a working position by one hand and to maintain them in position for screw with the workpiece by the power screwdriver, thus greatly shortening the required working time. Besides, the user can operate the power screwdriver by two hands to increase more safety for the operation.
U.S. Pat. No. 7,082,857 disclosed a portable screw driving tool including a housing portion, a feed tube mounted onto the housing portion, a slide body subassembly slidably mounted to the feed tube for forward and backward movement along the feed tube, and a sprocket mounted inside the slide body subassembly. The sprocket can be driven for rotation, while the slide body subassembly is moved backward, to drive a plastic strip in contact therewith to move forward along a predetermined path and then a plurality of screws carried by the plastic strip can be conveyed to a firing position one by one for screw with a workpiece by a drive bit of the portable screw driving tool.
The aforesaid portable screw driving tool further includes a movable guide defining a path that the plastic strip can be moved along. The movable guide is slidably mounted to the housing portion, having its front end fixed to the slide body subassembly whereby the movable guide is slidable forward and backward on the housing portion together with the slide body subassembly and then the plastic strip is also slidably moved to avoid bunching or tangling while the slide body subassembly is slidably moved.
Because the front end of the movable guide is fixed to the slide body subassembly and the primary part of the movable guide is mostly covered by the housing portion, the movable guide cannot be detached unless a tool is used and a lot of time is spent. In this way, the portable screw driving tool is too large to be conveniently portable for the user, also increasing the delivery cost.
The aforesaid portable screw driving tool further includes a spring located in the feed tube and having two ends contacting against the slide body subassembly and the housing portion respectively for pushing the slide body subassembly, the movable guide, the plastic strip, and the screws carried on the plastic strip back to the original position.
In such design, while the spring pushes the slide body subassembly, the movable guide, the plastic strip, and the screws back, the spring needs to overcome the resistance resulted from the forward movement of the plastic strip and the screws that are driven by the sprocket as well as the resistance resulted from the backward movement of the slide body subassembly, the movable guide, the plastic strip, and the screws. In this way, the spring is heavily loaded to cause unsmooth movement of the slide body subassembly, the movable guide, the plastic strip, and the screws and even to cause regular failure while the sprocket drives the plastic strip to further jam the screws while they are fed.